JP2011091212A - Superconducting magnet device and initial cooling method for superconducting coil of the same - Google Patents

Abstract

To provide a superconducting magnet device capable of shortening the cooling time of a superconducting coil from room temperature to a superconducting transition temperature while efficiently utilizing the heat of vaporization of liquid nitrogen, and an initial cooling method for the superconducting coil.
A superconducting magnet device includes a superconducting coil, a liquid nitrogen tank that is thermally connected to the superconducting coil at a lower end, and a liquid nitrogen introduction pipe that is connected to the liquid nitrogen tank. The nitrogen gas discharge pipe 11 connected to the liquid nitrogen tank 7, the temperature sensor 31 attached to the lower flange 22 of the liquid nitrogen tank 7, and the liquid nitrogen level sensor 32 attached to the upper flange 23 of the liquid nitrogen tank 7. And.
[Selection] Figure 2

Description

  The present invention relates to a cooling technique for a magnet device provided with a superconducting coil.

  The superconducting magnet device cools the superconducting coil to a cryogenic temperature and uses the superconducting coil in a superconducting state with zero electrical resistance. Since the superconducting coil is used in a superconducting state, there is no Joule heat generation, and a high magnetic field can be generated with less electric power than a normal conducting magnet device.

  Conventionally, as a cooling technique related to this type of superconducting magnet device, for example, there is one described in Patent Document 1. The superconducting magnet device described in Patent Document 1 is a conduction-cooling superconducting magnet device having a superconducting coil that can be cooled by a refrigerator, and a conductive cooling copper tube is spirally disposed on the outer periphery of the superconducting coil. It will be. The superconducting coil is cooled by introducing liquid nitrogen into the conductive cooling copper tube. And in patent document 1, it is called that the time concerning the initial cooling of a superconducting coil can be shortened by introduce | transducing liquid nitrogen in this copper pipe for conductive cooling.

  There is also a cooling technique as described in Patent Document 2. The superconducting magnet device described in Patent Document 2 includes a refrigerant container that is disposed in a radiation shield and is supplied with a refrigerant such as liquid nitrogen or liquid helium. This refrigerant container is thermally connected to the superconducting coil (see FIG. 14 of Patent Document 2). And in patent document 2, it is called that the cooling time of a superconducting coil can be shortened significantly by supplying refrigerant | coolants, such as liquid nitrogen and liquid helium, to the said refrigerant | coolant container, and pre-cooling a superconducting coil.

JP-A-6-132568 JP 2000-182821 A

  However, in the conduction cooling type superconducting magnet device described in Patent Document 1, when liquid nitrogen is introduced into the conduction cooling copper tube and the amount of liquid nitrogen introduced is small, liquid nitrogen is not present in the vicinity of the nitrogen inlet. However, nitrogen gas deprived of heat of vaporization by the superconducting coil is discharged from the nitrogen outlet of the conductive cooling copper pipe. That is, the superconducting coil portion located near the nitrogen outlet may be heated by the nitrogen gas deprived of vaporization heat. On the other hand, if the amount of liquid nitrogen introduced into the conductive cooling copper tube is too large, liquid nitrogen is discharged from the nitrogen discharge port, resulting in poor cooling efficiency. Thus, in the cooling technique described in Patent Document 1, it is very difficult to adjust the amount of liquid nitrogen introduced, and it is difficult to efficiently use the heat of vaporization of liquid nitrogen.

  The above problem is similarly present in the superconducting magnet device described in Patent Document 2. When liquid nitrogen is introduced into a refrigerant container thermally connected to the superconducting coil, if the amount of liquid nitrogen introduced is small, vaporization heat is taken away by the refrigerant supply pipe, and vaporization heat is taken inside the refrigerant container. Nitrogen gas (gaseous nitrogen) fills up. Here, in the cooling technique described in Patent Document 2, it is difficult to check whether or not liquid nitrogen is accumulated in the refrigerant container (whether the refrigerant container is filled with nitrogen gas).

  Further, if the temperature of the refrigerant container is lowered below the temperature at which nitrogen is solidified by the refrigerator, clogging with solid nitrogen may occur somewhere in the refrigerant supply pipe, the refrigerant container, and the refrigerant discharge pipe. If clogging occurs in the piping (refrigerant supply pipe or refrigerant discharge pipe), liquid nitrogen cannot be introduced and discharged, and the superconducting coil cannot be cooled using the vaporization heat of liquid nitrogen.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to reduce the cooling time of the superconducting coil from room temperature to the superconducting transition temperature while efficiently utilizing the heat of vaporization of liquid nitrogen. Another object is to provide a superconducting magnet device and an initial cooling method for the superconducting coil.

Means and effects for solving the problems

  To achieve the above object, the present invention provides a superconducting coil, a liquid nitrogen tank thermally connected to the superconducting coil at a lower end, a liquid nitrogen introducing pipe connected to the liquid nitrogen tank, A superconducting magnet apparatus comprising: a nitrogen gas discharge pipe connected to the liquid nitrogen tank; a temperature sensor attached to a lower end of the liquid nitrogen tank; and a liquid nitrogen level sensor attached to the liquid nitrogen tank. .

  According to this configuration, the liquid nitrogen introduced into the liquid nitrogen tank becomes nitrogen gas after the heat of vaporization is taken away by the superconducting coil in the lower part of the liquid nitrogen tank, and is discharged from the nitrogen gas discharge pipe. Here, whether or not liquid nitrogen is accumulated in the liquid nitrogen tank can be confirmed by a temperature sensor attached to the lower end of the liquid nitrogen tank. In addition, it can be confirmed whether or not liquid nitrogen is accumulated in the liquid nitrogen tank by a liquid nitrogen level sensor attached to the liquid nitrogen tank. That is, whether or not liquid nitrogen is accumulated in the liquid nitrogen tank can be reliably confirmed by the temperature sensor and the liquid nitrogen level sensor. Therefore, according to the present invention, liquid nitrogen that is always used for cooling the superconducting coil can be secured in the liquid nitrogen tank. As a result, the superconducting coil can be cooled while efficiently utilizing the heat of vaporization of liquid nitrogen, and the cooling time of the superconducting coil from room temperature to the superconducting transition temperature can be shortened.

  Moreover, in this invention, it is preferable that the said temperature sensor is inserted and attached to the hole formed in the lower end part of the said liquid nitrogen tank.

  According to this configuration, the temperature difference between the lower end of the liquid nitrogen tank and the temperature sensor can be reduced. That is, the temperature of the lower end portion of the liquid nitrogen tank can be measured more accurately, and as a result, the superconducting coil can be cooled while more efficiently using the heat of vaporization of liquid nitrogen.

  Furthermore, in the present invention, it is preferable that a gap filling material is inserted between the inner surface of the hole and the temperature sensor.

  According to this configuration, the temperature difference between the lower end of the liquid nitrogen tank and the temperature sensor can be reduced, and the temperature responsiveness of the temperature sensor is improved.

  Further, in the present invention, the hole has an opening into which the temperature sensor is inserted on a side surface of a lower end portion of the liquid nitrogen tank, and an air vent hole that allows the upper surface of the lower end portion of the liquid nitrogen tank to communicate with the hole. Is preferably further provided.

  According to this configuration, the temperature sensor can be prevented from coming off from the lower end of the liquid nitrogen tank when the superconducting magnet device is evacuated. Here, it is not easy to check whether or not the temperature sensor is disconnected from the lower end of the liquid nitrogen tank. If the temperature sensor is disconnected, the temperature at the lower end of the liquid nitrogen tank cannot be measured accurately. That is, according to the present invention, the temperature sensor can be prevented from coming off from the lower end of the liquid nitrogen tank, and as a result, the temperature of the lower end of the liquid nitrogen tank can be measured more accurately.

  Furthermore, in the present invention, it is preferable that the introduction port of the liquid nitrogen introduction pipe is disposed at the bottom of the liquid nitrogen tank.

  According to this configuration, when liquid nitrogen is introduced into the liquid nitrogen tank, liquid nitrogen can be gently introduced into the liquid nitrogen tank, and generation of useless vaporization heat can be suppressed. If this liquid nitrogen introduction pipe is used to discharge liquid nitrogen in the liquid nitrogen tank out of the tank, the introduction port is located at the bottom of the liquid nitrogen tank, so that all the liquid nitrogen in the liquid nitrogen tank Can be easily discharged out of the tank.

  Furthermore, in this invention, it is preferable to provide the refrigerator thermally connected with respect to the said superconducting coil. According to this configuration, the superconducting coil can be initially cooled by both the refrigerator and the liquid nitrogen tank. It should be noted that overcooling of liquid nitrogen (cooling below the temperature at which nitrogen solidifies) by the refrigerator can be prevented by measuring the temperature at the lower end of the liquid nitrogen tank with a temperature sensor.

  According to the second aspect of the present invention, there is provided an initial cooling method for the superconducting coil of the superconducting magnet device, wherein the amount of liquid nitrogen in the liquid nitrogen tank is determined by the temperature sensor and the liquid nitrogen level sensor. And cooling the superconducting coil by introducing liquid nitrogen from the liquid nitrogen introduction pipe to the liquid nitrogen tank while securing a predetermined amount of liquid nitrogen in the liquid nitrogen tank, and When the temperature of the superconducting coil is lowered to a predetermined temperature by the cooling process, the introduction of liquid nitrogen into the liquid nitrogen tank is stopped and helium gas is supplied to the liquid nitrogen tank, so that the inside of the liquid nitrogen tank is helium. A replacement step of substituting with gas, and discharging the helium gas in the liquid nitrogen tank to make the liquid nitrogen tank in a vacuum state And vacuum pull step, the initial cooling method of the superconducting coil of a superconducting magnet device provided with a.

  According to this configuration, the liquid nitrogen introduced into the liquid nitrogen tank by the cooling process becomes nitrogen gas after the vaporization heat is taken away by the superconducting coil in the lower part of the liquid nitrogen tank, and is discharged from the nitrogen gas discharge pipe. Go. Here, the amount of liquid nitrogen in the liquid nitrogen tank is detected by the temperature sensor and the liquid nitrogen level sensor, and by introducing liquid nitrogen into the liquid nitrogen tank while securing a predetermined amount of liquid nitrogen in the liquid nitrogen tank, The superconducting coil can be cooled while efficiently using the heat of vaporization of liquid nitrogen, and the cooling time of the superconducting coil from room temperature to the superconducting transition temperature can be shortened. In addition, after the cooling step, the superconducting coil can be prevented from being warmed by evacuating the liquid nitrogen tank through a replacement step with helium gas in the liquid nitrogen tank.

  In the present invention, an inlet of the liquid nitrogen introduction pipe is disposed at the bottom of the liquid nitrogen tank, and helium gas is supplied from the nitrogen gas discharge pipe to the liquid nitrogen tank in the replacement step. By discharging nitrogen from the liquid nitrogen introduction pipe, the nitrogen gas discharge pipe, the liquid nitrogen tank, and the liquid nitrogen introduction pipe are replaced with helium gas, and in the vacuum drawing step, the nitrogen gas discharge pipe, It is preferable that helium gas in the liquid nitrogen tank and in the liquid nitrogen introduction pipe is discharged to make the nitrogen gas discharge pipe, the liquid nitrogen tank, and the liquid nitrogen introduction pipe in a vacuum state.

  According to this configuration, since the inlet of the liquid nitrogen introduction pipe is disposed at the bottom of the liquid nitrogen tank, all the liquid nitrogen in the liquid nitrogen tank is removed in the replacement process with helium gas in the liquid nitrogen tank. It can be easily discharged out of the tank. Moreover, it is possible to further prevent the superconducting coil from being warmed by evacuating the inside of the nitrogen gas discharge pipe, the liquid nitrogen tank, and the liquid nitrogen introduction pipe.

It is a cross-sectional schematic diagram which shows the superconducting magnet apparatus which concerns on one Embodiment of this invention. It is a detailed sectional view of the A section shown in FIG.

  Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings.

(Configuration of superconducting magnet device)
FIG. 1 is a schematic cross-sectional view showing a superconducting magnet device 1 according to an embodiment of the present invention. As shown in FIG. 1, the superconducting magnet device 1 of this embodiment contains a superconducting coil 2, a liquid nitrogen tank 7 thermally connected to the superconducting coil 2, a superconducting coil 2, and a liquid nitrogen tank 7. A radiation shield 6 (cooling container), a vacuum container 5 for housing the radiation shield 6 in which the superconducting coil 2 and the liquid nitrogen tank 7 are housed, and a refrigerator 3 attached to the upper part of the vacuum container 5. .

(Superconducting coil)
The superconducting coil 2 has a winding frame 4 and a superconducting wire 16 wound around the winding frame 4 in a spiral shape. The winding frame 4 is made of a nonmagnetic material such as aluminum or stainless steel. The superconducting wire 16 is obtained by embedding, for example, a niobium-titanium (NbTi) alloy-based ultrafine multi-core wire in a copper base material. A cooling promoting member 8 is attached to the outer periphery of the superconducting coil 2. The cooling promotion member 8 is assembled in a cylindrical shape, and is attached so as to cover the entire superconducting wire 16. Examples of the material of the cooling promoting member 8 include a copper material.

(Liquid nitrogen tank)
FIG. 2 is a detailed cross-sectional view of part A shown in FIG. 1 and shows details of the liquid nitrogen tank 7. As shown in FIG. 2, the liquid nitrogen tank 7 includes a cylindrical tank body 21, a lower flange 22 (bottom plate) attached to the lower end of the tank body 21, and an upper flange 23 attached to the upper end of the tank body 21. (Top plate). The lower flange 22 and the upper flange 23 have a disk shape. Examples of the material of the liquid nitrogen tank 7 (the tank body 21, the lower flange 22, and the upper flange 23) include copper. Although the liquid nitrogen tank 7 is formed in a cylindrical shape, the liquid nitrogen tank 7 may be formed in a rectangular tube shape, or a conical tube shape (a cross-sectional area (a cross-sectional area in the horizontal direction) increases toward the lower side). May be formed.

  The liquid nitrogen tank 7 is thermally connected to the superconducting coil 2 at the lower end thereof. Specifically, a plate-shaped heat transfer member 9 is attached to the outer periphery of the cooling promotion member 8, and the lower flange 22 of the liquid nitrogen tank 7 is attached to the heat transfer member 9 by a fixing means such as a bolt. . Examples of the material of the heat transfer member 9 include a copper material. The heat transfer member 9 is disposed at the center of the superconducting coil 2 (or the cooling promoting member 8) in the height direction. From the viewpoint of cooling the superconducting coil 2 uniformly, it is preferable to arrange the heat transfer member 9 in the central portion of the superconducting coil 2 (or the cooling promoting member 8) in this way. In addition, it is not always necessary to arrange the heat transfer member 9 at the center in the height direction of the superconducting coil 2 (or the cooling promoting member 8).

  The liquid nitrogen introduction pipe 10 is connected to the upper flange 23 of the liquid nitrogen tank 7. The introduction port 10 a of the liquid nitrogen introduction pipe 10 is arranged at the bottom in the liquid nitrogen tank 7. A nitrogen gas discharge pipe 11 is connected to the upper flange 23 of the liquid nitrogen tank 7. The discharge port 11 a of the nitrogen gas discharge pipe 11 is located above the introduction port 10 a of the liquid nitrogen introduction pipe 10 and is disposed on the upper flange 23 (ceiling part) which is the uppermost end in the liquid nitrogen tank 7. ing. Examples of the material of the liquid nitrogen introduction pipe 10 and the nitrogen gas discharge pipe 11 include stainless steel.

  A liquid nitrogen level sensor 32 is attached to the upper flange 23 of the liquid nitrogen tank 7. The liquid nitrogen level sensor 32 is, for example, a capacitance type level sensor. As a level sensor (sensor type) that can be used as a liquid nitrogen level sensor other than the capacitance type level sensor, there are a semiconductor detection level sensor, an optical fiber type level sensor, and the like. A temperature sensor 31 is attached to the lower flange 22 (lower end) of the liquid nitrogen tank 7. 31 a is a lead wire of the temperature sensor 31. An example of the temperature sensor 31 is platinum resistance. The temperature sensor 31 may be attached to the lower end of the tank body 21.

  A hole 22a into which the temperature sensor 31 is inserted is provided on the side surface of the lower flange 22 (the hole 22a has an opening on the side surface of the lower flange 22). The shape and dimensions of the hole 22a are determined so that the temperature sensor 31 and the hole 22a are in close contact with each other. Thereby, the temperature difference between the lower flange 22 and the temperature sensor 31 can be reduced. As a result, the temperature of the lower end portion (lower flange 22) of the liquid nitrogen tank 7 can be accurately measured by the temperature sensor 31. It is desirable that a gap filling material (not shown) is inserted between the inner surface of the hole 22a and the temperature sensor 31. Examples of the gap filling material include Apiezon N grease and stycast. After applying Apiezon N grease, stycast, etc. to the inner surface of the hole 22a, the temperature sensor 31 is inserted into the hole 22a. Thereby, the temperature difference between the lower flange 22 and the temperature sensor 31 can be further reduced, and the temperature responsiveness of the temperature sensor 31 can be improved.

  The lower flange 22 is provided with an air vent hole 22b that allows the hole 22a and the upper surface of the lower flange 22 to communicate with each other. The air vent hole 22b is provided at the end of the hole 22a on the center side of the tank. The opening area of the air vent hole 22b (the opening area on the upper surface of the flange 22) is smaller than the opening area of the hole 22a (the opening area on the side surface of the lower flange 22). Note that the position of the air vent hole 22b is not necessarily limited to the position of this embodiment (the tank center side end of the hole 22a).

(Radiation shield)
The radiation shield 6 is a cooling container made of an aluminum material, a copper material, or the like. The liquid nitrogen introduction pipe 10 and the nitrogen gas discharge pipe 11 connected to the liquid nitrogen tank 7 are piped through the radiation shield 6 at a predetermined interval with respect to the superconducting coil 2. The liquid nitrogen introduction pipe 10 and the nitrogen gas discharge pipe 11 are fixed to the radiation shield 6 by a support member 15. Examples of the material of the support member 15 include stainless steel, aluminum, and copper. The inside of the radiation shield 6 is in a vacuum state.

(Vacuum container)
The vacuum container 5 is a container for keeping the inside thereof in a vacuum state and suppressing intrusion heat to the superconducting coil 2, the liquid nitrogen tank 7, the radiation shield 6, and the like. Examples of the material of the vacuum vessel 5 include an aluminum material and a stainless material. The outer surface of the vacuum vessel 5 is exposed to room temperature (about 300K).

(refrigerator)
The refrigerator 3 is a two-stage regenerative refrigerator, and includes a drive unit 12 and a cylinder 13 disposed below the drive unit 12. The cylinder 13 has an upper first cylinder 13a and a lower second cylinder 13b. A first cooling end 14a is provided at the lower end of the first cylinder 13a, and a second cooling end 14b is provided at the lower end of the second cylinder 13b. Each of the first cooling end portion 14a and the second cooling end portion 14b has a flange shape. The first cooling end portion 14a is attached to the radiation shield 6 by a fixing means such as a bolt, and the second cooling end portion 14b is attached to the heat transfer member 9 by a fixing means such as a bolt. Helium gas is supplied to the drive unit 12, and the supplied helium gas is ejected to the lower part of the first cylinder 13a and the lower part of the second cylinder 13b. The refrigerator 3 cools the radiation shield 6 and the superconducting coil 2 to about 40K and about 4K through the first cooling end 14a and the second cooling end 14b, respectively. The refrigerator 3 is thermally connected to the superconducting coil 2 via a cooling promotion member 8 and a heat transfer member 9.

(Initial cooling method for superconducting coils)
Next, an initial cooling method for the superconducting coil 2 of the superconducting magnet apparatus 1 will be described.

(Cooling process)
The cooling of the superconducting coil 2 is started using the refrigerator 3 and the liquid nitrogen tank 7. With respect to the refrigerator 3, the operation of the refrigerator 3 is started, and the superconducting coil 2 is cooled via the second cooling end portion 14 b and the heat transfer member 9. Regarding the liquid nitrogen tank 7, the superconducting coil 2 is cooled via the heat transfer member 9 by introducing liquid nitrogen 40 into the tank from the liquid nitrogen introduction pipe 10 connected to the liquid nitrogen tank 7. Here, the liquid nitrogen 40 is introduced into the liquid nitrogen tank 7 so that the temperature detected by the temperature sensor 31 attached to the lower end of the liquid nitrogen tank 7 is maintained at around 77K. This is for securing the liquid nitrogen 40 in the liquid nitrogen tank 7 and preventing the cooling of the liquid nitrogen 40 by the refrigerator 3 (cooling to a temperature below which the nitrogen solidifies).

  The liquid nitrogen 40 introduced into the liquid nitrogen tank 7 becomes nitrogen gas after the heat of vaporization is taken away by the superconducting coil 2 at the bottom of the liquid nitrogen tank 7, and the nitrogen arranged at the top of the liquid nitrogen tank 7. The gas is discharged from the discharge port 11a of the gas discharge pipe 11 to the outside. Here, whether or not a predetermined amount of liquid nitrogen 40 is accumulated in the liquid nitrogen tank 7 can be confirmed by measuring the temperature of the lower flange 22 with the temperature sensor 31 attached to the lower end of the liquid nitrogen tank 7. Further, the liquid nitrogen level sensor 32 attached to the liquid nitrogen tank 7 can also confirm whether or not a predetermined amount of liquid nitrogen 40 is accumulated in the liquid nitrogen tank 7. That is, the temperature sensor 31 and the liquid nitrogen level sensor 32 can reliably check whether or not the liquid nitrogen 40 is accumulated in the liquid nitrogen tank 7. Thereby, the liquid nitrogen 40 always provided for cooling the superconducting coil 2 can be secured in the liquid nitrogen tank 7. As a result, the superconducting coil 2 can be cooled while efficiently utilizing the heat of vaporization of the liquid nitrogen 40, and the cooling time of the superconducting coil 2 from room temperature to the superconducting transition temperature can be shortened. Since the nitrogen gas discharge pipe 11 is connected to the superconducting coil 2 at a predetermined interval, the superconducting coil 2 is prevented from being heated by the nitrogen gas deprived of vaporization heat.

  Further, since the introduction port 10a of the liquid nitrogen introduction pipe 10 is disposed at the bottom of the liquid nitrogen tank 7, when introducing the liquid nitrogen 40 into the liquid nitrogen tank 7, the liquid nitrogen 40 is gently removed from the liquid nitrogen tank 7. It can be introduced into the tank 7 and generation of useless vaporization heat can be suppressed.

  If the temperature detected by the temperature sensor 31 is higher than the predetermined temperature, the liquid nitrogen 40 is additionally introduced into the liquid nitrogen tank 7. Further, if the liquid nitrogen 40 level in the liquid nitrogen tank 7 becomes a predetermined level or less, the liquid nitrogen 40 may be additionally introduced into the liquid nitrogen tank 7. In addition, by attaching the liquid nitrogen level sensor 32, it is possible to prevent an excessive amount of liquid nitrogen 40 from being introduced into the liquid nitrogen tank 7.

  In addition, a control device (not shown) for controlling the amount of liquid nitrogen 40 in the liquid nitrogen tank 7 is provided, and signals from the temperature sensor 31 and the liquid nitrogen level sensor 32 are sent to the amount of liquid nitrogen 40 in the liquid nitrogen tank 7. It may be used for automatic control.

(Replacement process)
When the temperature of the superconducting coil 2 is reduced to about 77 K, the introduction of the liquid nitrogen 40 into the liquid nitrogen tank 7 is stopped and the helium gas is supplied to the liquid nitrogen tank 7, whereby the liquid nitrogen tank 7 is filled with helium gas. Replace with.

  Here, by supplying helium gas from the nitrogen gas discharge pipe 11 connected to the liquid nitrogen tank 7 to the liquid nitrogen tank 7 and discharging nitrogen from the liquid nitrogen introduction pipe 10, the liquid inside the nitrogen gas discharge pipe 11 is liquid. The inside of the nitrogen tank 7 and the inside of the liquid nitrogen introduction pipe 10 are replaced with helium gas. The temperature of the supplied helium gas is room temperature. Since the liquid nitrogen introduction pipe 10 and the nitrogen gas discharge pipe 11 may be clogged with nitrogen, it is once warmed with normal temperature helium gas to expel nitrogen. At this time, since the superconducting coil 2 is cooled to around 77K, the temperature rise due to the helium gas that expels nitrogen does not appear remarkably in the superconducting coil 2.

  Here, since the inlet 10a of the liquid nitrogen introduction pipe 10 is arranged at the bottom of the liquid nitrogen tank 7, the liquid nitrogen tank 7 is supplied by supplying helium gas from the nitrogen gas discharge pipe 11 to the liquid nitrogen tank 7. All the liquid nitrogen 40 can be easily discharged out of the tank.

(Vacuum drawing process)
When the inside of the liquid nitrogen tank 7 is replaced with helium gas, the helium gas in the liquid nitrogen tank 7 is discharged, and the inside of the liquid nitrogen tank 7 is evacuated. By entering a vacuum state, heat intrusion due to convection is prevented.

  Here, a vacuum citation pump (not shown) is connected to the liquid nitrogen introduction pipe 10 of the liquid nitrogen tank 7, and from the liquid nitrogen introduction pipe 10 to the nitrogen gas discharge pipe 11, the liquid nitrogen tank 7, and the liquid nitrogen introduction pipe. The helium gas in 10 is sucked and discharged by the vacuum reference pump, and the inside of the nitrogen gas discharge pipe 11, the liquid nitrogen tank 7, and the liquid nitrogen introduction pipe 10 are evacuated.

  By making the inside of the nitrogen gas discharge pipe 11, the inside of the liquid nitrogen tank 7 and the inside of the liquid nitrogen introducing pipe 10 into a vacuum state, it is possible to obtain a heat insulating effect and to further prevent the superconducting coil 2 from being warmed. Note that helium gas in the nitrogen gas discharge pipe 11, the liquid nitrogen tank 7, and the liquid nitrogen introduction pipe 10 may be sucked and discharged from the nitrogen gas discharge pipe 11 of the liquid nitrogen tank 7.

  When the evacuation process is completed, the initial cooling process of the superconducting coil 2 (superconducting magnet device 1) is completed, and thereafter, the superconducting coil 2 is cooled to the superconducting transition temperature by the refrigerator 3.

  The vacuum vessel 5 and the radiation shield 6 are also evacuated. Here, the hole 22a formed in the side surface of the lower flange 22 is provided with the air vent hole 22b at the end thereof as described above. The air vent hole 22b can prevent the temperature sensor 31 from coming off the lower flange 22 of the liquid nitrogen tank 7 when the radiation shield 6 is evacuated.

  Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications can be made as long as they are described in the claims. .

  For example, a plurality of liquid nitrogen tanks 7 may be equally arranged around the superconducting coil 2 and thermally connected to the superconducting coil 2. As a result, the number of liquid nitrogen tanks, liquid nitrogen introduction pipes, and nitrogen gas discharge pipes increases, but the entire superconducting coil 2 can be uniformly cooled, and the cooling efficiency can be improved.

1: Superconducting magnet device 2: Superconducting coil 3: Refrigerator 5: Vacuum vessel 6: Radiation shield (cooling vessel)
7: Liquid nitrogen tank 10: Liquid nitrogen introduction pipe 11: Nitrogen gas discharge pipe 22: Lower flange 31: Temperature sensor 32: Liquid nitrogen level sensor

Claims (8)

A superconducting coil;
A liquid nitrogen tank thermally connected at the lower end to the superconducting coil;
A liquid nitrogen inlet pipe connected to the liquid nitrogen tank;
A nitrogen gas discharge pipe connected to the liquid nitrogen tank;
A temperature sensor attached to the lower end of the liquid nitrogen tank;
A liquid nitrogen level sensor attached to the liquid nitrogen tank;
A superconducting magnet device. In the superconducting magnet device according to claim 1,
A superconducting magnet apparatus, wherein the temperature sensor is inserted and attached to a hole formed in a lower end portion of the liquid nitrogen tank. In the superconducting magnet device according to claim 2,
A superconducting magnet apparatus, wherein a gap filling material is inserted between an inner surface of the hole and the temperature sensor. In the superconducting magnet device according to claim 3,
The hole has an opening into which the temperature sensor is inserted on the side of the lower end of the liquid nitrogen tank,
A superconducting magnet apparatus, further comprising an air vent hole that allows the upper surface of the lower end of the liquid nitrogen tank to communicate with the hole. In the superconducting magnet device according to claim 1,
The superconducting magnet apparatus according to claim 1, wherein an inlet of the liquid nitrogen introduction pipe is disposed at a bottom portion in the liquid nitrogen tank. In the superconducting magnet device according to any one of claims 1 to 5,
A superconducting magnet device comprising a refrigerator thermally connected to the superconducting coil. An initial cooling method for a superconducting coil of the superconducting magnet device according to claim 1,
By detecting the amount of liquid nitrogen in the liquid nitrogen tank by the temperature sensor and the liquid nitrogen level sensor and securing a predetermined amount of liquid nitrogen in the liquid nitrogen tank, the liquid nitrogen tank is supplied from the liquid nitrogen introduction pipe. A cooling step of cooling the superconducting coil by introducing liquid nitrogen into
When the temperature of the superconducting coil is lowered to a predetermined temperature by the cooling step, the introduction of liquid nitrogen into the liquid nitrogen tank is stopped and helium gas is supplied to the liquid nitrogen tank, whereby the inside of the liquid nitrogen tank is A replacement step of replacing with helium gas;
Evacuation step of evacuating the liquid nitrogen tank by discharging the helium gas in the liquid nitrogen tank;
An initial cooling method for a superconducting coil of a superconducting magnet device. In the initial cooling method of the superconducting coil of the superconducting magnet device according to claim 7,
The inlet of the liquid nitrogen inlet pipe is disposed at the bottom of the liquid nitrogen tank;
In the replacing step, by supplying helium gas from the nitrogen gas discharge pipe to the liquid nitrogen tank and discharging nitrogen from the liquid nitrogen introduction pipe, the nitrogen gas discharge pipe, the liquid nitrogen tank, and the liquid Replace the nitrogen inlet tube with helium gas,
In the evacuation step, helium gas in the nitrogen gas discharge pipe, in the liquid nitrogen tank, and in the liquid nitrogen introduction pipe is discharged, and in the nitrogen gas discharge pipe, in the liquid nitrogen tank, and in the liquid nitrogen introduction pipe An initial cooling method for a superconducting coil of a superconducting magnet device, characterized in that a vacuum state is provided.

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